Mortimer, Leighton chairman for the past four years and a board member for 14, has been replaced by former Westfield chief executive Stephen Johns, while Stewart’s successor is Leighton Asia managing director Hamish Tyrwhitt.

Stewart could reasonably feel he has been treated as something of a scapegoat, given that the management decisions that have brought Leighton so much grief – chiefly, taking on stratospheric risks for minuscule margins at the multi-billion dollar Airport Link and Wonthaggi desalination plant projects – were made under the watch of his long-serving predecessor, Wal King.

Last year Mortimer had the tough task of persuading King to end his 23-year reign as CEO.

Ironically, media pundits are saying King was behind the scenes of Stewart’s and Mortimer’s axing, with the Australian reporting this morning “a palace coup orchestrated by [Leighton majority shareholder] Hochtief director Frank Stiehler and former boss Wal King” was responsible for the installation of Johns and King’s protege, Tyrwhitt.

With Tyrwhitt at the helm, Leighton’s work-in-hand in Asia has risen from $300 million to more than $6.6 billion in just four years. He has orchestrated some big contract mining wins for Leighton Contractors in Indonesia and Mongolia.

Clearly, Leighton and its European masters Hochtief and ACS believe there is more potential for growth in Asia and Tyrwhitt is the man to unlock it.

Incoming chairman Johns thanked Stewart for his “outstanding contribution” over 25 years with the company, which included a very successful stint at the helm of John Holland, but said “new leadership is now required for Leighton to move forward and capitalise on the significant growth opportunities that lie ahead”

Leighton Holdings posted an after-tax loss of $409 million for the 2010-11 financial year thanks to massive writedowns for the Airport Link and Vic Desal but expects to turn that into a $600-650 million profit next year.

Last month it lost a $1 billion-plus annual revenue stream when BHP Billiton bought out Leighton subsidiary HWE’s operations at three Western Australian iron ore mines.

Leighton shares slumped 5% to $20.25 this morning after Stewart’s departure was confirmed. It followed a 3.14% fall yesterday on news of Mortimer’s departure.

Leighton shares have nearly halved since November last year when the problems at Airport Link first came to light.